BlueTooth Technology

By Jith Crs

Bluetooth is the name given to a new technology standard using short-range radio links, intended to replace the cable(s) connecting portable and fixed electronic devices. The standard defines a uniform structure for a wide range of devices to communicate with each other.

Its important features of Bluetooth are robustness, low complexity, low power and low cost. Bluetooth is considered a wireless PAN technology that offers fast and reliable transmission for both voice and data. Bluetooth offers wireless access to LANs, PSTN, the mobile phone network and the Internet for home or office and other hand held devices.

A complete Bluetooth system will require these elements:

The lower-layer Bluetooth protocols are normally embedded in the baseband module, and the host processor must support the upper-layer protocols (like file transfer). In other words, the RF/baseband solution provides the means to communicate with the host, but need to implement a connection interface, as well as any upper-layer protocols, to use applications supported by the final product.

The higher/upper layers of the called as the Bluetooth profiles and these are nothing but a set of protocols. These protocols are optimized for particular applications. In the case of file transfer between two devices, it requires interoperability among devices. Each of the linked devices needs to have similar applications ensures interoperability across a spectrum of devices.

The Bluetooth stack: It has the following components:

The radio frequency (RF) portion provides the digital signal-processing (DSP) component of the system, and the baseband micro controller processes these signals. The link controller handles all the baseband functions and supports the link manager. It sends and receives data, identifies the sending device, performs authentication, and determines the type of frame to use for sending a transmissions. The link controller also directs how devices listen for transmissions from other devices and can move devices into sleep state in order to save power.

The link manager, located on top of the link controller, controls setup, authentication, link configuration, and other low-level protocols. Together, the baseband and the link manager establish connections for the network.

The host controller interface (HCI) communicates the lower-layer protocols to the host device(Like mobile phone, hand held PC etc).The host contains a processor.

L2CAP: it supports the upper-layer protocols and communicates with the lower layers. The Higher/upper-layer protocols consist of service-specific applications that must be integrated into the host application as explained above. RFCOMM protocol, which allows for the emulation of serial ports over the L2CAP, which is also an important part of Bluetooth.

The Service Discovery Protocol (SDP) gives the required services and the properties and characteristic of the service that a particular Bluetooth device is made for.

The ACL Link: Bluetooth uses five logical channels to support transferring of information between devices:

Core Protocols in Bluetooth:

Baseband: The Baseband and Link Control layer enables the physical RF link between Bluetooth forming a piconet. It provides two different kind of physical links with their corresponding baseband packets, Synchronous Connection-Oriented and Asynchronous Connectionless which can be transmitted in a multiplexing manner on the same RF link.Asynchronous Connectionless (ACL) packets are used for the transmission of data only while Synchronous Connection-Oriented can contain either audio or a combination of audio and information.

Link Manager Protocol: The link manager protocol is responsible for link set-up between Bluetooth devices. This includes setting up of security functions like authentication and encryption by generating, exchanging and checking of link and encryption keys and the control, negotiation of baseband packet sizes and duty cycles of the Bluetooth radio device, and the receiving device on the other end.

Logical Link Control and Adaptation Protocol: The Bluetooth logical link control and adaptation protocol (L2CAP) adapts upper layer protocols over the baseband. It can be thought to work in parallel with LMP in difference that L2CAP provides services to the upper layer when the payload data is never sent at LMP messages.

Service Discovery Protocol: Using SDP, device information, services and the characteristics of the services can be queried and after that, a connection between two or more Bluetooth devices can be established.

Telephony and Cable Replacement Protocol:

Telephony Control protocol: Binary (TCS Binary or TCS BIN), a bit oriented protocol, defines the call control signaling for the establishment of speech and data calls between Bluetooth devices.

RFCOMM:It is a serial line emulation protocol and is based on ETSI 07.10 ( European Telecommunications Standardization Institute ) specification. This protocol emulates RS-232 control and data signals over Bluetooth baseband, providing both transport capabilities for upper level services that use serial line as transport mechanism.

Adopted Protocols:

PPP:PPP is the IETF Point-to-Point Protocol (Internet Engineering Task Force, IETF Directory List of RFCs) and PPP-Networking is the means of taking IP packets to/from the PPP layer and placing them onto the LAN.

TCP/UDP/IP: TCP/IP/PPP is used for the all Internet Bridge usage scenarios in Bluetooth 1.0 and for OBEX in future versions. UDP/IP/PPP is also available as transport for WAP.

OBEX Protocol: IrOBEX (Short name is OBEX) is a session protocol developed by the Infrared Data Association (IrDA) to exchange data in a simple and automatic way.

Advantages:

Using peer-to-peer connectivity, simplifies personal area wireless connections, enabling all digital devices to communicate automaticaly. also provides fast, secure voice and data transmissions. The range for connectivity is less than 10 meters, and line of sight is not required. The Bluetooth radio unit can functions even in noisy radio environments, ensuring audible voice transmissions in severe conditions. It can protect data by using error-correction methods and provides a high transmission rate. It is possible encryption and authentication for privacy in the transmitted data.

In Bluetooth ad hoc networking enables personal devices to automatically exchange information and synchronize with each other.

Jith is an Electrical and Electronic Engineer by profession from Southern india. he has good experience in sensors, Data acquisition systems, communication protocols etc, and can be contact through crsjith@gmail.com

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